Currently, with the increasing incidence of cancer and the increasing concerns about antibiotic residual in animal feeds, researchers around the world are eager to find a safe and effective functional agent which improves the patients' immunity, so as to diagnose or treat diseases.
Cell-wall polysaccharides of microorganisms (especially yeasts) are regarded as a best choice. Upon entering the intestinal tract, the yeast glucan and mannan may be absorbed into the human body via intestinal epithelium through endocytosis, and play an effective role in enhancing the immunity of animal and human body, improving the intestinal function and resisting radiation. Its mechanism of action includes stimulating and activating macrophages, NK cells and other immunocytes, promoting the release of cytokines, and killing the tumor cells, antigens and other harmful particles directly or indirectly. In addition, they can adsorb various toxins in the intestinal tract due to their excellent capability of adsorbing, enhance the intestinal peristalsis and improve the intestinal function.
Glucan and mannan are the major components of microbial (particularly, yeast) cell walls. Glucan, as a glucose polymer, is an alkali insoluble polysaccharide with β-1,3-glucan as the backbone and minor β-1,6-detran as side chains. On the other hand, mannan is water soluble polysaccharide has α-1,6-bonded D-mannose as the backbone, with most or even all of the mannose molecules having side chains composed of 2-5 α-1,2- or α-1,3-linked mannose residues.
Multiple researches have been carried out regarding the extraction and utilization of cell wall glucan. However, these researches show several disadvantages: (1) the extraction method relates mainly to simple treatments with acid or alkali, and the glucan content of the preparations is lower than 60%; (2) substantial researches focus on the extraction of glucan, other than the simultaneous extraction of glucan and mannan (most of which is discarded); (3) some of the processes are not suitable for large-scale applications in industry, with low stability and yield.
In view of the diverse application of yeast cells in the fermentative industry and the various utilization of β glucan, novel methods for preparing glucan from yeast cells are needed in the art. These new methods shall overcome the disadvantages of low stability and/or low yield in the prior art.